Homothetic perfect fluid space-times

A brief summary of results on homotheties in General Relativity is given, including general information about space-times admitting an r-parameter group of homothetic transformations for r>2, as well as some specific results on perfect fluids. Attention is then focussed on inhomogeneous models, in particular on those with a homothetic group $H_4$ (acting multiply transitively) and $H_3$. A classification of all possible Lie algebra structures along with (local) coordinate expressions for the metric and homothetic vectors is then provided (irrespectively of the matter content), and some new perfect fluid solutions are given and briefly discussed.Comment: 27 pages, Latex file, Submitted to Class. Quantum Gra

Aquatic food security:insights into challenges and solutions from an analysis of interactions between fisheries, aquaculture, food safety, human health, fish and human welfare, economy and environment

Fisheries and aquaculture production, imports, exports and equitability of distribution determine the supply of aquatic food to people. Aquatic food security is achieved when a food supply is sufficient, safe, sustainable, shockproof and sound: sufficient, to meet needs and preferences of people; safe, to provide nutritional benefit while posing minimal health risks; sustainable, to provide food now and for future generations; shock-proof, to provide resilience to shocks in production systems and supply chains; and sound, to meet legal and ethical standards for welfare of animals, people and environment. Here, we present an integrated assessment of these elements of the aquatic food system in the United Kingdom, a system linked to dynamic global networks of producers, processors and markets. Our assessment addresses sufficiency of supply from aquaculture, fisheries and trade; safety of supply given biological, chemical and radiation hazards; social, economic and environmental sustainability of production systems and supply chains; system resilience to social, economic and environmental shocks; welfare of fish, people and environment; and the authenticity of food. Conventionally, these aspects of the food system are not assessed collectively, so information supporting our assessment is widely dispersed. Our assessment reveals trade-offs and challenges in the food system that are easily overlooked in sectoral analyses of fisheries, aquaculture, health, medicine, human and fish welfare, safety and environment. We highlight potential benefits of an integrated, systematic and ongoing process to assess security of the aquatic food system and to predict impacts of social, economic and environmental change on food supply and demand

New family of inhomogeneous γ\gamma-law cosmologies: example of gravitational waves in a homogeneous p=ϱ/3p=\varrho/3 background

We present an explicit three-parameter class of $p=\gamma \varrho$, ($-1/3\leq\gamma<1$), cosmological models admitting a two-dimensional group $G_{2}$ of isometries acting on spacelike surfaces. The family is self-similar in the sense that it has a further homothetic vector field and it contains subfamilies of both (previously unknown) tilted and non-tilted Bianchi models with that equation of state. This is the first algebraically general class of solutions of this kind including dust inhomogeneous solutions. The whole class presents a universal spacelike big-bang singularity in the finite past. More interestingly, the case $p=\varrho /3$ constitutes a new two-parameter inhomogeneous subfamily which can be viewed as a Bianchi V background with a gravitational wave travelling orthogonally to the surfaces of transitivity of the $G_{2}$ group. This wave generates the {\it inhomogeneity} of the spacetime and is related to the sound waves {\it tilting} the perfect fluid. It seems to be the first explicit exact example of a gravitational wave travelling along a homogeneous background that has a realistic equation of state $p=\varrho /3$.Comment: LaTeX, 25 pages, 3 figures. Uses epsfig package. One reference added; minor changes. To appear in Phys.Rev.

Leisure Behavior Pattern Stability During the Transition from Adolescence to Young Adulthood

Leisure is an important context in which human development occurs. Changes in leisure behavior patterns may indicate changing developmental needs or reflect contextual changes that impact leisure behavior. The transition from adolescence to young adulthood provides an excellent opportunity for the study of the stability of leisure behavior as individuals' contexts are changed with the adoption of adult roles and the potential for disruption of leisure patterns exists. Previous studies investigating leisure and the transition from adolescence to young adulthood have tended to be cross-sectional and focus on specific leisure behaviors rather than identifying patterns of leisure behavior. The present study involved a longitudinal investigation of leisure behavior patterns over a three-year period during the transition from adolescence to young adulthood, and determined the nature of leisure pattern stability and instability during this period. In general, leisure pattern stability was the most common pathway into young adulthood. The patterns of leisure behavior and the nature of the changes that occurred with the transition from adolescence to young adulthood differed to some degree for males and females, although similarities in patterns and transitions were also found.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45285/1/10964_2004_Article_411255.pd

The Early Royal Society and Visual Culture

Recent studies have fruitfully examined the intersection between early modern science and visual culture by elucidating the functions of images in shaping and disseminating scientific knowledge. Given its rich archival sources, it is possible to extend this line of research in the case of the Royal Society to an examination of attitudes towards images as artefacts –manufactured objects worth commissioning, collecting and studying. Drawing on existing scholarship and material from the Royal Society Archives, I discuss Fellows’ interests in prints, drawings, varnishes, colorants, images made out of unusual materials, and methods of identifying the painter from a painting. Knowledge of production processes of images was important to members of the Royal Society, not only as connoisseurs and collectors, but also as those interested in a Baconian mastery of material processes, including a “history of trades”. Their antiquarian interests led to discussion of painters’ styles, and they gradually developed a visual memorial to an institution through portraits and other visual records.AH/M001938/1 (AHRC

Past horrors, present struggles: The role of stigma in the association between war experiences and psychosocial adjustment among former child soldiers in Sierra Leone

Upon returning to their communities, children formerly associated with armed forces and armed groups--commonly referred to as child soldiers--often confront significant community stigma. Much research on the reintegration and rehabilitation of child soldiers has focused on exposure to past war-related violence and mental health outcomes, yet no empirical work has yet examined the role that post-conflict stigma plays in shaping long-term psychosocial adjustment. Two waves of data are used in this paper from the first prospective study of male and female former child soldiers in Sierra Leone. We examined the role of stigma (manifest in discrimination as well as lower levels of community and family acceptance) in the relationship between war-related experiences and psychosocial adjustment (depression, anxiety, hostility and adaptive behaviors). Former child soldiers differ from one another with regard to their post-war experiences, and these differences profoundly shape their psychosocial adjustment over time. Consistent with social stress theory, we observed that post-conflict factors such as stigma can play an important role in shaping psychosocial adjustment in former child soldiers. We found that discrimination was inversely associated with family and community acceptance. Additionally, higher levels of family acceptance were associated with decreased hostility, while improvements in community acceptance were associated with adaptive attitudes and behaviors. We found that post-conflict experiences of discrimination largely explained the relationship between past involvement in wounding/killing others and subsequent increases in hostility. Stigma similarly mediated the relationship between surviving rape and depression. However, surviving rape continued to demonstrate independent effects on increases in anxiety, hostility and adaptive/prosocial behaviors after adjusting for other variables. These findings point to the complexity of psychosocial adjustment and community reintegration in these youth and have a number of programmatic and policy implications.War Mental health Children Adolescents Child soldiers Trauma Stigma Sierra Leone